1. Field of the Invention
The present invention relates to a medical guidewire used for medical purposes such as inserting a catheter into a blood vessel, a ureter, or an organ or inserting an indwelling device into part of a blood vessel suffering from an aneurysm.
2. Description of the Related Art
In general, it is required that a medical guidewire have a flexible distal end portion. In order to fulfill such a requirement, a guidewire 100 of the related art includes a core shaft 101 and a coil spring 102 that surrounds the core shaft 101, and the diameter of a distal end portion 103 of the core shaft 101 is made small so as to improve flexibility (see FIG. 4).
When using the guidewire 100 to guide a device, such as a catheter or an indwelling device, to a target region in a human body, the distal end portion of the guidewire 100 may be unintentionally bent into a U-shape. For some operations, the guidewire 100 is bent into a U-shape before insertion in order to prevent misinsertion of the guidewire 100 into a nontarget blood vessel or in order that the guidewire 100 is securely held by a blood vessel wall by using the resilience of the guidewire 100.
The guidewire 100 of the related art has a low rigidity because the diameter of the distal end portion 103 of the core shaft 101 is small, so that the guidewire 100 is easily bent due to stress concentration. Once the core shaft 101 is bent into a U-shape, plastic deformation occurs, so that the core shaft 101 has a residual angle even after the U-shaped bending is released. Due to the presence of the residual angle, the operability of the guidewire 100 is reduced, and the guidewire 100 may have to be replaced during the operation.
It is required that the guidewire 100 have a flexible and resilient distal end portion, and it is also required that the guidewire 100 has a good torque transmission with which an operation performed at the proximal end portion is smoothly transmitted to the distal end portion.
A modification of the guidewire 100 uses a stranded wire as the distal end portion 103 of the core shaft 101 (see Japanese Unexamined Patent Application Publication No. 2008-161491). The guidewire 100 has a certain degree of resilience after having been bent. However, when the guidewire 100 is bent into a U-shape having a large curvature, the guidewire 100 may not recover its original shape even after the U-shaped bending is released. Therefore, the drawback due to the presence of a residual angle remains.
Another modification of the guidewire 100 includes a radiopaque inner coil disposed between the coil spring 102 and the core shaft 101 (see Japanese Unexamined Patent Application Publication No. 08-173547 and Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2006-511304). With the guidewire 100, the rigidity of a part of the distal end portion 103 having the inner coil is increased. However, this modification also has the drawback due to the presence of a residual angle after having been bent into a U-shape.